Optimisation and Understanding of Plasma Enhanced Atomic Layer Deposition Processes Using Quasi In-situ X-ray Photoelectron Spectroscopy

Atomic layer deposition (ALD) is a variant of chemical vapor deposition where precursors and coreactants are admitted to the reaction chamber in sequence, with purge steps in between. The techqniue allows for atomic layer thickness control, and conformal coating over large areas and structures with high aspect ratios at the nano scale. Plasma Enhanced ALD is a modification of the technique where the co-reactant step is replaced with an RF plasma exposure. Plasma enhanced (PE)-ALD processes allow for lower processing temperatures due the increased surface reactivity afforded by the plasma, which is particularly important for CMOS applications with a low thermal budget. The films also show improved growth rate control, density, and precursor ligand incorporation.

In this work we report on improving the understanding of plasma enhanced ALD processes through the use of an x-ray photoelectron spectroscopy system which is coupled in vacuum by a robotic handler to a commercial ALD system. The system allows for half-cycle resolution analysis of ALD processes without exposure to atmosphere and contamination by adventitious carbon and oxygen. Our experiments show that carbon and oxygen in ALD grown films which is often attributed to contamination in the literature is as a result of ligand incorporation and that tuning of the plasma parameters can be used to optimise the films. We also show that traditional depth profiling techniques such as ion sputtering can lead to incorrect inferences about the chemistry of thin films.

We focus on the growth of TiO₂ by both thermal and plasma enhanced ALD to illustrate the differences. We also present work on the the growth of nickel metal and nickel oxide as well as cobalt metal and cobalt nitride from nickelocene and cobaltocene precursors respectively, highlighting how PE-ALD can be used to yield metal and nitride films. Finally we will present some results on non-ALD plasma processing carried out in the integrated analysis tool.